This is a modification of my grandmothers traditional chile rellenos recipe. Note that the traditional recipe calls for beaten egg whites instead of the flour/soymilk batter and cheese instead of tofu. The recipe sounds a lot more complicated than it actually is!
Roast chiles* until skin begins to blister on all sides (this will require turning the chiles). You can do this over an open flame or on a cast-iron skillet. (I prefer to use a comal - a flat cast-iron skillet.) Set chiles aside to cool.
In a small pan, simmer diced onion, cumin, salt and pepper in olive oil until the onions become translucent. (You can also add chili powder if you prefer.) Add tomato sauce. Simmer, stirring occasionally, for at least 20 minutes, but preferably longer.
In a small mixing bowl, whisk flour, soymilk, and pinch of salt. The batter should be thick, but not so thick that you can't move a whisk through it easily. (You might have to adjust the flour/soy milk ratio accordingly.) Set aside.
Slice tofu into 3/8 slices.
Peel the cooled chiles.* The skin should pull off easily. (Dont worry, the chiles aren't hot; you'll be able to touch your contact lenses and eyes without any irritation.) Using a small knife, core the chiles, seeds and all, by slicing off the stem side.
Stuff the chiles with one slice of tofu, dip in batter, and fry in vegetable oil until each side is golden. Set on dry paper towels to drain excess oil.
Serve the chile rellenos with a dollop of the tomato sauce and enjoy!
* If using canned chiles, skip this step.